Puzzle ZNTM 

Workings

Hint
A little algebra might help.

Answer
Pineapple = 83p, coconut = 57p, melon = 62p.

Reasoning
If we assign the letters P, C and M to the fruits, and work in pence we have:

(1)   M + C = 119
(2)   M + P = 145
(3)   C + P = 140

Using (2) - (1) we have:

(4)   P - C = 26

And (3) + (4) gives:

         2P = 166
          P = 83

This can then be substituted back into (2) and (3).